For a wide variety of applications, chairs are nowadays provided with features which provide enhanced comfort to the person using the chair. For illustration, office-type chairs are commonly utilized in modern working environments to provide an occupant with a level of comfort while performing certain tasks that require a person to be in a seated position for an extended period of time. One common configuration for such a chair includes a mobile chair base assembly to allow the chair to roll across a floor and a pedestal column supporting the superstructure of the chair. The superstructure may include components which enable the user to adjust certain settings of the chair and to facilitate recline or “tilt” of the chair superstructure, including the seat and back of the chair. This basic chair configuration allows users to change their sitting position in the chair as desired, such that fatigue may be minimized during long sitting periods.
In recent years, chair designs have implemented a feature where a chair back and seat both move simultaneously during a tilting or rearwardly reclining motion of the chair back. The chair seat may also tilt in this process or may be displaced otherwise relative to the chair base. The combined movement of the chair back and seat in these designs results in some level of improvement for the occupant through a range of tilting motions over a conventional “static” chair without coordinated back and seat movement.
Various configurations may be realized to implement such a coordinated motion of the chair back and chair seat. For illustration, a back support supporting the chair back may be coupled to a seat support supporting the chair seat via a pivot coupling.
Such a pivot coupling may restrict the movement of the rear portion of the seat to a radial movement. Such a purely radial movement may give rise to undesired conditions, such as “shirt shear” or “bridging” conditions. If a shirt sear occurs, the occupant's shirt may be untucked, which is undesirable. When the bridging condition occurs, the lower portion of the chair back falls away from the occupant during recline. In such a condition, the occupant's lumbar region may be largely unsupported by the chair back.
More complex configurations of tilt mechanisms may be realized, in order to make it less likely for undesired conditions to occur during recline. For illustration, the reclining mechanism may be provided with an additional link member which is coupled to the seat support through a pivot connection and to the back support through another pivot connection. While more complex relative movements of the chair seat and chair back can be defined using such configurations, they may lead to increased complexity and, thus, costs of the tilt mechanism. Further, considerable re-design may be required to adapt such a tilt mechanism to various types of chairs.
It may also be desirable to implement a chair tilt mechanism which can be easily adapted to different chair requirements. Different types of chairs may impose different constraints on the mechanism. For illustration, the chair tilt mechanism should be able to move between the zero tilt and the full tilt position, while not moving the occupant's center of gravity relative to the chair base assembly so much that an overbalancing or tipping occurs. The shift in center of gravity which is still acceptable will depend on the configuration of the chair base assembly. Complex configurations of chair superstructures, for example of the type using additional link members articulated to both the seat support and the backrest support, may be complicated to re-design so as to accommodate the design constraints imposed by different types of chairs.